FIG. 1 shows a conventional head-up display apparatus of this kind. In FIG. 1, a dash board 2 is disposed in front of a driver's seat 1 of a vehicle, and a projector 6 composed of a light source 3, a display device 4 and a lens 5 is disposed within the dash board 2. An image of a display pattern on the display device 4 of the projector 6 is reflected by a front glass 7 and is visualized as a virtual image 8 in front of the front glass 7.
The display device 4 is generally constituted by a fluorescent lamp display tube, a an LED, a liquid crystal display (LCD), etc. In the case of LCD, a display pattern is projected onto the front glass 7 by light illuminated and penetrated from a rear portion of the apparatus. The lens 5 enlarges the virtual image 8 of the projected display pattern, and forms the image 8 in predetermined positions in front of the front glass 7.
In the head-up display apparatus for a vehicle, a driver visually overlaps an outer landscape through the front glass 7 and a displayed image so that it is not necessary to move the driver's line of sight during the operation of the vehicle, thereby rapidly reading the display and safely driving the vehicle.
However, in the conventional head-up display apparatus, since the image is directly projected from an upper face of the dash board onto a face of the front glass 7, the optical path from the dashboard to the projected face is short so that the display image 8 is formed in a relatively close position in front of the front glass 7. As a result, the driver must repeatedly focus the outer landscape and the displayed image 8 so that a suitable visuality cannot be obtained and the driver's eyes are tired. It is considered that another lens is inserted into the optical path to form the displayed image 8 distantly. However, such an arrangement increases the cost of the apparatus, which is not preferable.
Another conventional display apparatus is disclosed in Japanese Laid-Open 50-48576 for example. In this example, as shown in FIG. 2, an apparatus has a projector attached to a dashboard 51a of a vehicle 51 and composed of a light source 53, a convex lens 54, and a display unit 55 for displaying speed information, etc., of the vehicle 51, which are stored within a casing 52 of the apparatus.
An image Q.sub.1 displayed in the display unit 55 is projected through the convex lens 54 onto a half mirror 57 as a reflecting member disposed near a front glass 56, and a virtual image Q.sub.2 is formed in front of the half mirror 57.
In such a conventional apparatus, as shown in FIGS. 3A and 3B, the half mirror 57 is moved around a vertical axis 59 and a horizontal axis 60 in the right-left direction "a" and forward-backward direction "b" to adjust the angle of the reflecting member such that the virtual image Q.sub.2 formed in front of the front glass 56 can be visualized in a predetermined position irrespective of different positions and drivers of varying heights and/or physique 58. The adjusted position of the reflecting member is fixed by rotating individual thumbscrews respectively disposed with respect to the horizontal and vertical axes 59 and 60. Accordingly, it is necessary to operate the two thumbscrews before and after the adjustment of the position of the reflecting member so that it is laborious to operate these thumbscrews and the number of parts is increased, and the apparatus is complicated, and it takes time to manufacture and assemble the apparatus, thereby increasing the cost thereof.